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The arrival of humans around 50,000 years ago[2][3]
and settlement by Europeans
from 1788, has had a significant impact on the flora. The use of fire-stick farming
by Aboriginal people led to significant changes in the distribution of plant species over time, and the large-scale modification or destruction of vegetation for agriculture and urban development since 1788 has altered the composition of most terrestrial ecosystems, leading to the extinction of 61 plant species and endangering over 1000 more.

Australia was part of the southern supercontinent
Gondwana, which also included
South America,
Africa,
India
and Antarctica. Most of the modern Australian flora had their origin in Gondwana during the
Cretaceous
when Australia was covered in subtropical rainforest. Australian ferns and gymnosperm bear strong resemblance to their Gondwanan ancestors,[4]
and prominent members of the early Gondwanan angiosperm flora such as the Nothofagus,
Myrtaceae
and Proteaceae
were also present in Australia.[5]

Gondwana began to break up 140 million years ago (MYA); 50 MYA during the
Eocene
Australia separated from Antarctica, and was relatively isolated until the collision of the Indo-Australian Plate
with Asia in the Miocene
era 5.3 MYA. As Australia drifted, local and global
climate change
had a significant and lasting effect: a circumpolar oceanic current developed, atmospheric circulation increased as Australia moved away from Antarctica, precipitation fell, there was a slow warming of the continent and arid
conditions started to develop.[6]
These conditions of geographic isolation and aridity led to the development of a more complex flora. From 25-10 MYA pollen records suggest the rapid radiation of species like Eucalyptus,
Casuarina,
Allocasuarina,
Banksia
and the pea-flowered legumes, and the development of open forest; grasslands started to develop from the
Eocene. Collision with the
Eurasian Plate
also led to additional South-east Asian
and cosmopolitan
elements entering the flora like the Lepidium
and Chenopodioideae.[7]

The development of aridity and the old and nutrient poor soils of the continent led to some unique adaptations in the Australian flora and evolutionary radiation of genera – like
Acacia
and Eucalyptus
– that adapted to those conditions. Hard leaves with a thick outer layer, a condition known as
scleromorphy, and
C4
and CAM
carbon fixation which reduce water loss during photosynthesis are two common adaptations in Australian arid-adapted dicot and monocot species respectively. Rising aridity also increased the frequency of fires in Australia. Fire is thought to have played a role in the development and distribution of fire-adapted species from the Late Pleistocene. An increase in charcoal in sediment around 38,000 years ago coincides with dates for the inhabitation of Australia by the
Indigenous Australians
and suggests that man-made fires, from practices like fire-stick farming, have played an important role in the establishment and maintenance of sclerophyll forest, especially on the east coast of Australia.[8]
Adaptations to fire include lignotubers
and epicormic buds in Eucalyptus
and Banksia
species that allow fast regeneration following fire. Some genera also exhibit serotiny, the release of seed only in response to heat and/or smoke.
Xanthorrhoea
grass trees and some species of orchids only flower after fire.[9]

According to the scheme the most common vegetation types are those that are adapted to arid conditions where the area has not been significantly reduced by human activities such as land clearing for agriculture. The dominant vegetation type in Australia is the hummock grasslands that occur extensively in arid Western Australia, South Australia and the Northern Territory. It accounts for 23% of the native vegetation, the predominant species of which are from the genus
Triodia.
Zygochloa
also occurs in inland sandy areas like the Simpson Desert.

A further 39% of native vegetation is covered by a combination of:

Eucalypt woodlands found at the transition between hummock grasslands and higher rainfall areas where conditions still limit tree growth; the woodland may have a grass or shrubby understory. The largest area is in Queensland.

Acacia shrublands in semi arid and arid regions. The most common are mulga shrublands; the largest area is in Western Australia.

Tussock grasslands that occur in semi-arid and some temperate
[clarification needed]
parts of Australia; they host a large variety of grasses from more than 10 genera. The largest area is in Queensland.

Other groups with restricted areas of less than 70,000 square kilometres include tropical or temperate rainforest and vine thickets, tall or open eucalypt forests,
Callitris
and Casuarina forests, and woodlands and heath.

Australia has over 30,000 described species of vascular plants, these include the
angiosperms, seed-bearing non-angiosperms (like the conifers and cycads), and the spore-bearing ferns and fern allies.[12]
Of these about 11% are naturalised species; the remainder are native or endemic.[13]
The vascular plant flora has been extensively catalogued, the work being published in the ongoing Flora of Australia
series. A list of vascular plant families represented in Australia using the Cronquist system
is also available.[14]

At the higher taxonomic levels the Australian flora is similar to that of the rest of the world; most vascular plant families are represented within the native flora, with the exception of the
cacti,
birch
and a few others, while 9 families occur only in Australia.[15][16]
Australia's vascular flora is estimated to be 85% endemic;[17]
this high level of vascular plant endemism is largely attributable to the radiation of some families like the Proteaceae,
Myrtaceae, and
Fabaceae.

The native Australian flora contains many
monocotyledons. The family with the most species is the
Poaceae
which includes a huge variety of species, from the tropical bamboo Bambusa arnhemica
to the ubiquitous spinifex that thrives in arid Australia from the genera Triodia
and Plectrachne. There are more than 800 described species of
orchid
in Australia.[18]
About one quarter of these are epiphytes. The terrestrial orchids occur across most of Australia, the majority of species being deciduous
– their aboveground parts die back during the dry season and they re-sprout from a tuber when it rains.

Many plant families that occur in Australia are known for their floral displays that follow seasonal rains. The
Asteraceae
is well represented by its subfamily Gnaphalieae, which included the paper or everlasting daisies; this group has its greatest diversity in Australia. Other families with flowering shrubs include the
Rutaceae, with the fragrant
Boronia
and Eriostemon, the
Myoporaceae
with the Eremophila, and members of the
Ericaceae
with Victoria's Floral Emblem Epacris impressa.

Aquatic moncots and dicots both occur in Australian waters. Australia has about 51,000 square kilometres of
seagrass
meadows and the most diverse group seagrass species in the world. There are 22 species found in temperate waters and 15 in tropical waters out of a known 70 species worldwide.[20]
Aquatic dicots include the mangroves; in Australia there are 39 mangrove species that cover 11,500 square kilometres and comprise the third largest area of mangroves in the world.[21]
Other native aquatic dicots here include water lilies
and water milfoils.

Gymnosperms
present in Australia include the cycads
and conifers. There are 69 species of cycad from 4 genera and 3 families of eastern and northern Australia, with a few in south-western Western Australia and central Australia[clarification needed]. Native pines are distributed through 3 families
[clarification needed], 14 genera and 43 species, of which 39 are endemic. Most species are present in wetter mountainous areas consistent with their Gondwanan origins, including the genera
Athrotaxis,
Actinostrobus,
Microcachrys,
Microstrobos,
Diselma
and the Tasmanian Huon pine, sole member of the genus
Lagarostrobos.
Callitris
is a notable exception; species from this genus are found mainly in drier open woodlands.[22]
The most recently discovered species of conifer is the living fossilWollemi pine, which was first described in 1994.

Spore bearing vascular plants include the
ferns
and fern allies. True ferns are found over most of the country and are most abundant in tropical and subtropical areas with high rainfall. Australia has a native flora of 30 families, 103 genera and 390 species of ferns, with another 10 species being naturalised. The fern allies are represented by 44 native species of
psilophytes,
horsetails
and lycophytes.[22]
Ferns prefer a cool and damp environment since water is required for reproduction, the majority of Australian species are found in bushland [clarification needed]
and rainforest, there are aquatic, epiphytic (Platycerium,
Huperzia
and Asplenium), and terrestrial species including large tree ferns from the genera
Cyathea
and Dicksonia.

The
algae
are a large and diverse group of photosynthetic organisms. Many studies of algae include the cyanobacteria, in addition to micro and macro
eukaryotic
types that inhabit both fresh and saltwater. Currently, about 10,000 to 12,000 species of algae are known for Australia.[23]
The algal flora of Australia is unevenly documented: northern Australia remains largely uncollected for seaweeds and marine phytoplankton, descriptions of freshwater algae are patchy, and the collection of terrestrial algae has been almost completely neglected.[24]

The
bryophytes
– mosses,
liverworts
and hornworts
– are primitive, usually terrestrial, plants that inhabit the tropics, cool-temperate regions and montane areas; there are some specialised members that are adapted to semi-arid and arid Australia. There are slightly fewer that 1,000 recognised species of moss in Australia. The five largest genera are the Fissidens,
Bryum,
Campylopus,
Macromitrium
and Andreaea.[25]
There are also over 800 species of liver- and horn-worts in 148 genera in Australia.[26]

The fungal flora of Australia is not well characterised; Australia is estimated to have about 250,000 fungal species of which roughly 5% have been described. Knowledge of distribution, substrates and habitats is poor for most species, with the exception of common plant pathogens.[27]

Lichens
are composite organisms comprising, in most cases, an Ascomycete fungus and a unicellular green alga, their classification is based on the type of fungi. The lichen flora of Australia and its island territories, including Christmas Island,
Heard Island,
Macquarie Island
and Norfolk Island, currently comprises 3,238 species and infra-specific taxa in 422 genera, 34% of which are considered to be endemic.[28]

The first Australian plants recognised and classified in Linnaean taxonomy were a species of
Acacia
and Synaphea
in 1768 as Adiantum truncatum
and Polypodium spinulosum
respectively by Dutch philologist Pieter Burman the Younger, who stated they were from Java. Later, both were found to be from Western Australia, likely to have been collected near the Swan River, possibly on a 1697 visit there of fellow Dutchman
Willem de Vlamingh.[29]
This was followed by Cook's
expedition making landfall at what is now Botany Bay
in April 1770, and the early work of Banks, Solander and Parkinson.[who?]
Botanical exploration was enabled by the founding of the permanent colony at Port Jackson in 1788, and the subsequent expeditions along Australia's coastline.[29]

The Australian flora was utilised by the
Indigenous inhabitants
of Australia. Indigenous Australian's used thousands of species for food, medicine, shelter, tools and weapons.[30]
For example, the starchy roots of Clematis microphylla
were used in western Victoria to make a dough that was baked, and the leaves of the plant were used as a poultice applied to skin irritations and blisters.[31]

The changes since 1788 have been rapid and significant: displacement of Indigenous Australians disrupted fire régimes that had been in place for thousands of years; forestry practices have modified the structure of native forests; wetlands have been filled in; and broad scale land-clearing for crops, grazing and urban development has reduced native vegetation cover and led to landscape salinisation, increased sediment, nutrient and salt loads in rivers and streams, loss of habitat and a decline in biodiversity.[34]
The intentional and unintentional release of invasive
plant and animal species into delicate ecosystems is a major threat to floral biodiversity; 20 introduced species have been declared Weeds of National Significance.[35]

Protected areas
have been created in every state and territory to protect and preserve the country's unique ecosystems. These protected areas include national parks and other reserves, as well as 64 wetlands registered under the Ramsar Convention
and 16 World Heritage Sites. As of 2002, 10.8% (774,619.51 km²) of the total land area of Australia is within protected areas.[37]
Protected marine zones have been created in many areas to preserve marine biodiversity; as of 2002, these areas cover about 7% (646,000 km²) of Australia's marine jurisdiction.[38]

The Australian Government's Threatened Species Scientific Committee has identified 15
biodiversity hotspots
in Australian and 85 characteristic ecosystems, as classified by the Interim Biogeographic Regionalisation for Australia, cover the continent; some effort is being made to ensure each is represented within a protected area under Australia's Biodiversity Action Plan.[39][40]

Jump up
^Crisp, M. et al. 2004. Radiation of the Australian flora: what can comparisons of molecular phylogenies across multiple taxa tell us about the evolution of diversity in present-day communities?
Philosophical Transactions of the Royal Society of London. Series B - Biological Sciences
359: 1551-1571

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^Singh, G. et al. 1981. Quaternary vegetation and fire history in Australia. In A. M. Gill, R. A. Groves and I. R. Nobel.
Fire and the Australian Biota.
Australian Academy of Science, 23-54

Jump up
^Gill, A. M. 1981. Adaptive responses of Australian vascular plant species to fire. In A. M. Gill, R. H. Groves, and I. R. Noble. eds.
Fire and the Australian Biota. Australian Academy of Science

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^ESD Working Group on Biological Diversity. 1991.
The Conservation of Biological Diversity as it Relates to Ecologically Sustainable Development, Report of Working Party to the Ecologically Sustainable Development Secretariat, Canberra.

^
Jump up to:
abGeorge, A. S. (1981). "The genus
Banksia
L.f. — a case history in Australian botany". History in the service of systematics : papers from the Conference to celebrate the centenary of the British Museum (Natural History. London: Society for the Bibliography of Natural History. pp. 53–59.
ISBN0-901843-05-9.

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^Williams J. 2000, Managing the Bush: Recent research findings from the EA/LWRRDC National Remnant Vegetation R&D Program, National Research and Development Program on Rehabilitation, Management and Conservation of Remnant Vegetation, Research Report 4/00.